This project involves systematic study of two kinds of attention dysfunction. Pathologies of selective attention and vigilance were observed in early clinical descriptions of schizophrenia. The purpose of this study is to investigate whether these attention deficits may be specific to schizophrenia and may be potential markers of predisposition to schizophrenia. Selective attention will be measured by the dichotic listening task and vigilance by crossover reaction time. Both tasks have proven their sensitivity in discriminating schizophrenics from controls. Aspects of performance will be examined for which schizophrenics perform in a qualitatively different manner than controls, since such indices appear relatively free of contamination by general deficits. Further, various improved procedures will be implemented to obtain more sensitive, reliable measures that are matched on discrminating power to elicit specific rather than general effects. The project entails three studies. In Study I, the dichotic shadowing task will be administered to 125 normal individuals of a broad range of abilities in order to match the no distraction and distraction conditions on discriminating power. Study II will compare the performance of normal controls with that of schizophrenic, bipolar depressed and nonpsychotic patients to determine whether performance deviations are specific to schizophrenia. Study III will contrast the performance of relatives of schizophrenics, relatives of bipolar affectives, and relatives of non-psychotic patients to determine whether the laboratory tasks may be potential markers of vulnerability to schizophrenia. Findings should enhance understanding of the exact nature and interrelationships among attention dysfunctions in schizophrenia, their diagnostic specificity, and potential merit as markers of predisposition to schizophrenia.